I. Field of the Invention
The invention relates to a drilling device which is lowered into a drill hole to be driven into hard stone, particularly rock, and to a process for drilling the hole.
II. Description of the Prior Art
Drilling devices are known which consist of a drive means, a drill which is rotated by the drive means and a clamping device which can be engaged with the internal wall of the drill and/or its pipe wall and serving to transfer the torque of the drive means to the drill and which are connected as a unit and can be fastened to a hoist rope or a drilling linkage with the drill being movable compared with the clamping device by an amount equal to one work stroke in an axial direction to the drill. German Pat. No. 842 932 describes such a drilling device which can execute one work stroke under the influence of its own weight wherein the clamping device via a limited work stroke is guided axially but rotatably along the housing containing the drive motor and carrying a gimlet bit. As a rule, the weight of the drilling device suffices for drilling in a loose soil, possibly containing small sized stones; however, when drilling in hard stone, particularly in bedrock, this weight does not suffice to remove the stone especially if a gimlet bit or a box-shaped drill is equipped with cutters at the bottom. German Published Application No. 27 22 075 shows such a drilling device equipped with a gimlet bit where piston-cylinder elements are arranged between the clamping device and the drive motor of the drill in an axial direction to the drill hole in order to increase the pressure of the drill provided by the weight of the drilling device. This measure only facilitates faster drilling in loose soil, but the device is also unsuited for drilling in bedrock. German Pat. No. 1 171 848 cited in the above-mentioned German Publication is an internal drilling device with a rotary drill drive used with the reverse flushing process where an additional active drill pressure via hydraulic piston-cylinder arrangements is also exerted. For the above-mentioned reasons, this known version is also unsuited for drilling in very hard stone.
German Published Application No. 28 45 878 describes a drilling device for in-ground drilling where the advancing movement of the drilling device is implemented by kellies whereas the rotary movement is caused by a drive motor attached at the lower end of the linkage. This drilling device is intended for general in-ground drilling and represents an improvement compared with the previously known drilling devices of this type where the advance as well as the rotary drive of the drill is transmitted by telescoping kelly rods whereas in accordance with the version of the Published Application the kellies do not participate in the rotary movement since the rotary drive is implemented by the drive motor connected with the drill to form one unit and the drilling linkage is handled by a carrying or support device above the drive hole. In spite of this, it is necessary to install the required linkage from the drilling device to the carrier device for the flush as well as for dry drilling which is rather expensive depending upon depth of the drilling. Another factor is that the augers in a core drill and the roller bits of a drill which removes the entire drilled matter require very high rotary forces for cutting in bedrock so that the necessary linkages must be correspondingly strong and therefore correspondingly expensive.
All of the versions of the above described published applications have the same drawback, namely, that they can be used successfully for drilling in soft to hard and rock soil, but that they can work in medium hard to hard rock only with very low drilling output with high energy expenditure, and that this also can be facilitated only with limited drilling depth.